Method and an arrangement for management of bearers

ABSTRACT

The invention is directed to a method for management of bearers in cellular telecommunication systems in such a situation, when the demand of services is greater than the capacity of the network to provide such services. According to the invention, a set of priority values is associated with each bearer. Preferably, the set of priority values comprises an absolute priority value, which is the same for all bearers associated with a certain USIM, and a relative priority value, which defines the priority order of the bearers associated with a certain USIM. The network uses these priority values to determine, which bearer is dropped, when not enough resources are available.

This application claims the benefit of the earlier filed InternationalApplication No. PCT/FI99/00636, International Filing Date, 22 Jul. 1999,which designated the United States of America, and which internationalapplication was published under PCT Article 21(2) in English as WOPublication No. WO 00/05913.

TECHNICAL FIELD OF THE INVENTION

The invention is directed to a method and an arrangement for managementof bearers in cellular telecommunication systems in such a situation,when the demand of services is greater than the capacity of the networkto provide such services.

BACKGROUND OF THE INVENTION

For clarification of common terms used in this document, an overview ofcertain cellular telecommunication system configurations is presented inthe following.

Proposals for third-generation systems include UMTS (Universal MobileTelecommunications System) and FPLMTS/IMT-2000 (Future Public LandMobile Telecommunications System/International Mobile Telecommunicationsat 2000 MHz). In these plans cells are categorised according to theirsize and characteristics into pico-, nano-, micro- and macrocells, andan example of the service level is the bit rate. The bit rate is thehighest in picocells and the lowest in macrocells. The cells may overlappartially or completely and there may be different terminals so that notall terminals necessarily are able to utilise all the service levelsoffered by the cells.

FIG. 1 shows a version of a future cellular radio system which is notentirely new compared with the known GSM system but which includes bothknown elements and completely new elements. In current cellular radiosystems the bottleneck that prevents more advanced services from beingoffered to the terminals comprises the radio access network RAN whichincludes the base stations and base station controllers. The corenetwork of a cellular radio system comprises mobile services switchingcentres (MSC), other network elements (in GSM, e.g. SGSN and GGSN, i.e.Serving GPRS Support Node and Gateway GPRS Support node, where GPRSstands for General Packet Radio Service) and the related transmissionsystems. According e.g. to the GSM+ specifications developed from GSMthe core network can also provide new services.

In FIG. 1, the core network of a cellular radio system 930 comprises acore network CN 931 which has three parallel radio access networkslinked to it. Of those, net-works 932 and 933 are UMTS radio accessnetworks and network 934 is a GSM radio access network. The upper UMTSradio access network 932 is e.g. a commercial radio access network,owned by a telecommunications operator offering mobile services, whichequally serves all subscribers of said telecommunications operator. Thelower UMTS radio access network 933 is e.g. private and owned e.g. by acompany in whose premises said radio access network operates. Typicallythe cells of the private radio access network 933 are nano- and/orpicocells in which only terminals of the employees of said company canoperate. All three radio access networks may have cells of differentsizes offering different types of services. Additionally, cells of allthree radio access networks 932, 933 and 934 may overlap either entirelyor in part. The bit rate used at a given moment of time depends, amongother things, on the radio path conditions, characteristics of theservices used, regional overall capacity of the cellular system and thecapacity needs of other users. The new types of radio access networksmentioned above are called generic radio access networks (GRAN). Such anetwork can co-operate with different types of fixed core networks CNand especially with the GPRS network of the GSM system. The genericradio access network (GRAN) can be defined as a set of base stations(BS) and radio network controllers (RNC) that are capable ofcommunicating with each other using signaling messages. Below, thegeneric radio access network will be called in short a radio networkGRAN.

The terminal 935 shown in FIG. 1 is preferably a so-called dual-modeterminal that can serve either as a second-generation GSM terminal or asa third-generation UMTS terminal according to what kind of services areavailable at each particular location and what the user's communicationneeds are. It may also be a multimode terminal that can function asterminal of several different communications systems according to needand the services available. Radio access networks and services availableto the user are specified in a subscriber identity module 936 (SIM)connected to the terminal.

In UMTS specifications, a SIM is denoted with the term USIM (UMTS SIM).One mobile communication means (ME, mobile equipment) such as a cellulartelephone can have more than one USIM connected to the terminal. This isuseful, for example, for providing a person with a private telephonenumber with a first USIM and another number for work-related calls witha second USIM. The person can then receive calls to all of thesetelephone numbers with the same ME comprising the two USIMs, and bar anycalls to any of these telephone numbers at his/her leisure. For example,the person can bar any calls to the work-related number at weekends andallow only calls to his/her private number. The USIMs may be separate ICcards, whereby the ME is required to have more than one USIM connectorfor connecting the USIMs, or a single IC card may comprise more than onelogical USIMs.

In cellular telecommunication systems a single speech connection or dataconnection through the cellular telecommunication network is called abearer. Generally, a bearer is associated with a set of parameterspertaining to data communication between a certain terminal equipmentand a network element, such as a base station or an interworking unit(IWU) connecting the cellular network to another telecommunicationsnetwork. The set of parameters associated with a bearer comprisestypically for example data transmission speed, allowed delays, allowedbit error rate (BER), and the minimum and maximum values for theseparameters. A bearer may further be a packet transmission bearer or acircuit switched bearer and support for example transparent ornon-transparent connections. A bearer can be thought of as a datatransmission path having the specified parameters connecting a certainmobile terminal and a certain network element for transmission ofpayload information. One bearer always connects only one mobile terminalto one network element. However, a bearer can pass through a number ofnetwork elements. One mobile communication means (ME, Mobile Equipment)may in some cellular telecommunication systems support one bearer only,in some other systems also more than one simultaneous bearers.

One old problem in cellular telecommunication systems is how to handlesituations, in which the demand of services at some area in a cellulartelecommunication system exceeds the capability of the cellulartelecommunication system to provide such services. This problem is moresevere in the UMTS system presently under development and other systems,where a mobile communication means (ME) can have more than onesimultaneus connections i.e. bearers. A method is needed fordetermining, which current bearers are dropped or which new bearers areallowed in an overload situation.

One example of a typical overload situation is the handover of aconnection to a crowded cell. One conventional way of handling thissituation is simply to refuse the handover, which may result in a brokenconnection. The situation is more complicated, if the ME has severalconnections, and the new cell has spare capacity for only a subset ofthose connections. In such a situation, a method is needed for selectingwhich connections are serviced and which connections are refused.

One further example of a problematic situation is such a situation, whenthe capacity of a cell is already in full use, and one ME requests forexample an increase in data transmission rate or a group of new bearers.

SUMMARY OF THE INVENTION

An object of the invention is to alleviate problems associated with celloverload situations. A further object of the invention is to realize amethod for selection of bearers, which are to be denied of service in anoverload situation. An object of the invention is also to realize amethod for priorizing of bearers.

The objects are reached by defining a multilevel priority scheme forbearers, which allows flexible allocation of resources for bearershaving widely differing parameters.

The method according to the invention for management of bearers in acellular telecommunications system is characterized by that

-   -   at least two priority data items are associated with each        bearer, and    -   decisions whether or not to provide services for a bearer are        based at least in part on the value of at least one of said at        least two priority data items.

The cellular telecommunications system according to the invention ischaracterized by that for management of bearers

-   -   at least two priority data items are arranged to be associated        with each bearer, and    -   decisions whether or not to provide services for a bearer are        arranged to be based at least in part on the value of at least        one of said at least two priority data items.

A radio network controller according to the invention for a cellulartelecommunications system is characterized by that for management ofbearers it comprises

-   -   means for associating at least two priority data items with each        bearer, and    -   means for making decisions whether or not to provide services        for a bearer based at least in part on the value of at least one        of said at least two priority data items.

The dependent claims describe further advantageous embodiments of theinvention.

The invention relates to alleviating problems in those situations, wherea radio access network cannot support all present or requested bearers.According to the invention, a set of priority values is associated witheach bearer. Preferably, the set of priority values comprises anabsolute priority value, which is the same for all bearers associatedwith a certain USIM, and a relative priority value, which defines thepriority order of the bearers associated with a certain USIM. Thenetwork uses these priority values to determine, which bearer isdropped, when not enough resources are available.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in more detail in the following withreference to the accompanying drawings, of which

FIG. 1 illustrates the general structure of a cellular telecommunicationnetwork according to prior art,

FIG. 2 illustrates one example of selection of bearers to be servicedaccording to an advantageous embodiment of the invention,

FIG. 3 illustrates one example of signalling according to anadvantageous embodiment of the invention,

FIG. 4 illustrates one example of a telecommunications system and aradio network controller according to the invention.

Same reference identifiers are used for similar entities in the figures.

DETAILED DESCRIPTION

According to an advantageous embodiment of the invention, a two-levelpriority scheme is used. For each client identity, an absolute priorityvalue is assigned, and for each bearer, a relative priority value. Sucha two-level priority scheme using two priority data items allows on theone hand treatment of all bearers of a client identity as a single uniton a client-by-client basis, and on the other hand treatment of allbearers of all client identities on a bearer-by-bearer basis.

Treatment of all bearers of a client identity as a single unit can beeffected by using only one of the priority values as the basis forbearer servicing decisions. Preferably, the absolute priority associatedwith the client identity is used as the basis for decisions. Treatmentof all bearers of a client identity as a single group is useful e.g. inhandover situations, when the network decides, whether or not to allow ahandover to occur.

In some situations it is advantageous to prioritize the use oftransmission capacity on a bearer-by-bearer basis. In such cases, boththe absolute and the relative prioritization can be used for selectingthe bearers to be dropped first. Advantageously, those bearers whichhave the lowest relative priority of the client identitites havinglowest absolute priority, are dropped first. Such an approach isadvantageous for example in air interface congestion situations.

The client identity referred to in the previous paragraphs is in anadvantageous embodiment of an invention the identity of a single USIM,as the following examples in the description of various figures of thisspecification show. However, the invention is not limited to such anembodiment. A client identity can also comprise multiple USIMs. Forexample, a client identity may also refer to a single ME having multipleUSIMs, whereby the client identity comprises multiple USIM identities.

The absolute priority value of each USIM may advantageously be stored inthe USIM. The absolute priority value may be different between differentUSIMs, also in cases where a single ME comprises more than one USIMs.Further, an operator may set the price of an USIM according to theabsolute priority level of the USIM. The absolute priority is preferablythe same for all bearers associated with the same USIM. The relativepriority value can advantageously be used to distinguish the bearersassociated with the same USIM. This relative priority value of eachbearer can advantageously be assigned automatically during the setup ofthe bearer, for example, by the call control entity for that particularUSIM.

FIG. 2 illustrates selection of serviced bearers according to anadvantageous embodiment of the invention. FIG. 2 shows three mobilecommunication means ME1,ME2,ME3 which already have connections to a basestation. In this example, we assume that the base station is able tosupport eight bearers. As shown in FIG. 2, the first mobile ME1 has twoUSIMs USIM11, USIM12, the second mobile ME2 one USIM USIM21 and thethird mobile ME3 one USIM USIM31. In the initial situation as shown bythe left side of the figure, the first mobile ME1 has four bearers,three of the bearers associated with the first USIM USIM11 and one withthe second USIM USIM12. The second mobile ME2 has only one bearer, andthe third mobile ME3 two bearers. The bearers have two priority levels,the higher level called the absolute priority A3,A5 being associatedwith the USIM and the lower level called the relative priority R1,R2,R3being associated with each bearer. As one can see from FIG. 2, the threebearers associated with USIM11 have the lowest absolute priority valueA5, while the other bearers have a middle priority of A3. In the exampleof FIG. 2, it is assumed that the absolute priority values range from A1to A5, the latter being the lowest priority.

The range of priority values is not limited in any way by the presentinvention. The range may comprise more or less than five values, and theorder of priority values may be different from that explained in theprevious paragraph.

At this initial situation, a fourth mobile ME4 is switched on, and theuser of ME4 wishes to start communication using two bearers for exampleto have a video telephone call. Consequently, ME4 signals a request tothe network to set up two bearers. Alternatively, ME4 could represent amobile moving from another cell towards the cell servicing ME1, ME2, andME3, and require a handover.

The USIM of ME4 has the absolute priority level A3 associated with it.Upon reception of the request, the network examines the bearer situationof the base station and finds out, that only one more bearer can beaccommodated. Since two bearers were requested, one bearer must bedenied service, either one of the requested bearers or one of currentlyserviced bearers. In this case, there are three currently active bearershaving a lower absolute priority value than the requested bearers,namely the bearers of ME1 associated with the first USIM USIM11 of ME1.Consequently, the network decides to drop the bearer having the lowestrelative priority value among the three bearers BEARER111, BEARER112,BEARER113 of USIM11, thereby creating free capacity to accommodate therequested two new bearers of ME4. As a result, the bearer situation ofthe base station becomes as shown in the right side of FIG. 2.

The selection of bearers may in various embodiments of the invention bedifferent from that shown in the example of FIG. 2. In one advantageousembodiment of the invention where all bearers of a client identity suchas a USIM are treated in a single group, all bearers of the first USIMUSIM11 of ME1 are dropped instead of only one as shown in FIG. 2, sincethey have the lowest absolute priority value of all active bearers andbearer requests.

Advantageously, each USIM has an associated default absolute prioritylevel, which is assigned to each new bearer. In further advantageousembodiments of the invention, a user can change the priority settings ofhis/her connections to ensure that he/she receives the desired servicefrom the network. Naturally, the network operator may change the chargeslevied per connection time or per transmitted amount of data as a resultof change of priority settings. Advantageously, the user may change theabsolute priority level of any of his/her USIMs, and the relativepriority level of any active bearer. Further, the user may change thedefault priority levels, or the desired priority level for the nextconnection requested. In further advantageous embodiments, the user maychange the priorities of currently active bearers during the connection.Changing of priority of currently active bearers is advantageous forexample when the user is downloading a large file to the ME, and wishesto speed up the process by temporarily increasing the priority of thebearer.

On the other hand, the network may start to select the bearers to beserviced for many reasons. For example, when the air interface becomescongested at a so called hot spots, for example during mass events whenlarge crowds of people are present at one location, the network mayincrease the required priority levels to cope with the overload. Afurther example is a decrease of the capacity of a base station due toe.g. malfunctioning of a transmitter of the base station.

In an overload situation, the network may offer a possibility to theuser to choose to increase the priority level and accept higherconnection charges in order to avoid termination of his/her connections.In an advantageous embodiment of the invention, the user may set defaultpreferences for his/her USIMs specifying, if and within which limits thepriority levels of the user's connections may be automatically changedduring overload situations.

In various embodiments of the invention, the user may adjust any of thepriority values. The user may, for example, increase the absolutepriority values to increase the service level of all of his bearers.Naturally, the network operator may adjust the charges accordingly.

In one advantageous embodiment, the operator may set a required minimumpriority for a certain cell or for any number of cells or even for thewhole network, which minimum priority must be matched or exceeded inorder to obtain any service from the network.

In another advantageous embodiment of the invention, the bearer requestdoes not contain an explicit indication of a priority. Instead, thenetwork chooses the priority based on the information contained in thebearer request, for example the type of bearer requested. For example,if the user requests an expensive service, the network chooses arelatively high priority to be used for that bearer.

As previously described, a user may advantageously change the priorityvalues during a connection. For example, during a multimedia sessiondifferent multimedia components, each one forming a separate bearer, areoften added or removed, whereby the preferences given at call setup mayno longer correspond to the current wish of the user. The user maytherefore wish to modify the relative priority of his/her bearers. Oneexample of a signalling procedure for priority modification according toan advantageous embodiment of the invention is shown in FIG. 3. THEconnections are controlled by the Call Control (CC) entities in the corenetwork. The decisions on whether or not to provide radio service for abearer are made in the radio access network RAN. The priority values arestored in the RAN. FIG. 3 shows the signalling between a call controlentity ME-CC 10 in a mobile communication means, a corresponding peerentity CN-CC 20 in the core network, and the radio access network RAN30. After the user instructs the mobile communication means to increasethe priority of a bearer, the ME-CC 10 sends a MODIFY_(—)REQUEST message110 to the CN-CC 20. The CN-CC invokes a priority modification procedurein the radio access network RAN 30 by sending a MODIFY_(—)PRIORITYmessage 120 to the radio access network RAN 30. After receiving theMODIFY_(—)PRIORITY command, the radio access network modifies 130 thepriority of the bearer as desired. When the radio access network hascompleted the priority modification, it sends 140 an acknowledgementMODIFY_(—)PRIORITY_(—)ACK message back to CN-CC. The CN-CC finishes themessaging by sending 150 an acknowledgement MODIFY_(—)REQUEST_(—)ACKmessage to ME-CC.

A terminal can modify several bearers substantially simultaneously byinitiating the negotiation procedure separately for each bearer insuccession. In another advantageous embodiment, a list of beareridentities is attached as a parameter to the MODIFY REQUEST message.

FIG. 4 shows an example of a telecommunications system and a radionetwork controller according to the invention. The radio networkcomprises radio network controllers RNC1, RNC2 and RNC3. Base stationsBS1, BS2 and BS3 are controlled by the radio network controller RNC0,base stations BS4, BS5 and BS6 re controlled by the radio networkcontroller RNC1, and base stations BS7, BS8 and BS9 are controlled bythe radio network controller RNC2. A mobile equpiment ME is connected byradio to the system, via the base stations and radio networkcontrollers. In FIG. 4 the base station BS5 is active, ie. the datatransfer between the system and the mobile equipment is routed via thebase station BS5. There can also be several active base stations, ifmacro diversity is used. It should be noted that FIG. 4 shows only afraction of the usual number of radio network controllers and basestations in a radio network.

The radio network controller may comprise the following logical units.The logical link control LLC controls the radio connections between theradio network controller and a mobile equipment. The tasks of thelogical link control LLC may include error detection, error correctionand retransmission in error situations. In addition, the logical linkcontrol LLC may comprise control for the necessary buffers andacknowledge windows. The macrodiversity controller MDC performs thefunctions that belong to macrodiversity combining according to thepossible macrodiversity implementation used. The set controller SCcontrols the active set of base stations. The radio network controlleraccording to the invention also comprises means PM for associatingpriority data items with a bearer, and means DM for making decisionswhether or not to provide services for the bearer based on the value ofthe priority data items. The means PM and DM can be realized as parts ofother logical means of the radio network controller, or they can beseparate logical means in the radio network controller.

The invention is not limited to using a two-level priority scheme asexplained in the previous examples. For example, in an advantageousembodiment of the invention, a three-level priority scheme is used, i.e.three priority data items are associated with each bearer. In such anembodiment, the highest level priority value is associated with the ME,the middle level priority value is associated with each USIM connectedwith the ME, and the lowest level priority value is associated with thebearers of the USIMs. In such an embodiment, the selection of bearers tobe serviced may proceed in a way analogous to the selection in atwo-level scheme, e.g. starting the dropping of bearers from that groupof bearers which has lowest values of the two higher priority levels,and dropping first those bearers having the lowest bearer-associatedpriority level. Further, a three-level priority scheme is advantageousfor example when a ME comprising more than one USIM attempts to performa handover to another cell. In such a situation it is advantageous, thatall bearers of the ME can be treated as a single group when the networkdetermines, whether or not to allow the handover to occur. In such asituation the ME advantageously has a priority value associated to it,which value is used by the network in said determination.

The priority scheme according to the invention can also be used in othersituations than network overload situations. For example, instead ofaffecting the selection of bearers denied or allowed, the priorities mayalso affect the service level such as transmission capacity allocatedfor a bearer. For example, by setting the priority levels of his bearershigh enough, the user may obtain better and faster service than otherusers with lower priority levels. With the inventive priority scheme, auser may obtain almost any service level he desires, and can adjust theobtained service level at any time by adjusting the priority values. Thepriority scheme further allows the network to reduce the level ofservice given to bearers having low priority, and thus avoid an overloadsituation altogether.

The name of a given functional entity, such as the radio networkcontroller, is often different in the context of different cellulartelecommunication systems. For example, in the GSM system the functionalentity corresponding to a radio network (RNC) is the base stationcontroller (BSC). Further, the various command names such as theMODIFY_(—)REQUEST command name are intended to be examples only, and theinvention is not limited to using the command names recited in thisspecification.

In view of the foregoing description it will be evident to a personskilled in the art that various modifications may be made within thescope of the invention. While a preferred embodiment of the inventionhas been described in detail, it should be apparent that manymodifications and variations thereto are possible, all of which fallwithin the true spirit and scope of the invention.

1. A method for management of bearers in a cellular telecommunicationssystem, characterized in that at least two priority data items areassociated with each bearer, the first one of the priority data itemshaving a same value for at least two bearers associated under the sameclient identity, decisions whether or not to provide services for abearer are based at least in part on the value of at least one of saidat least two priority data items, bearers are organized into sets on atleast two hierarchical levels and a priority data item is given for eachset, and all bearers associated with the same client identity have thesame values of a first priority data item of said at least two prioritydata items; and wherein when considering the denial of services betweenfirst and second bearers, the service is denied for the bearer with alower value of the first priority data item, disregarding their valuesof a second priority data item, unless the bearers have the same valuefor the first priority data item, then the service is denied for thebearer with a lower value of a second priority data item.
 2. A methodaccording to claim 1, characterized in that one of the hierarchicallevels is the level of one bearer, and the sets on that level compriseone bearer.
 3. A method according to claim 1, characterized in that oneof the hierarchical levels is the level of client identity, and the setson that level comprise the bearers of that client identity.
 4. A methodaccording to claim 1, characterized in that at least two sets ofdecisions on providing service are defined, a first combination of thepriority data items is used in a first set and a second combination ofthe priority data items is used in a second set.
 5. A method accordingto claim 1, characterized in that the value of the first priority dataitem is stored in the USIM.
 6. A method according to claim 1,characterized in that said client identity is the identity of a USIM. 7.A method according to claim 1, characterized in that at least one of thepriority data items is allocated during the bearer setup procedure.
 8. Amethod according to claim 1, characterized in that at least one prioritydata item is changed during the connection.
 9. A method according toclaim 7, characterized in that the priority data item is determined bythe mobile station.
 10. A method according to claim 7, characterized inthat the priority data item is determined by the network.
 11. A methodaccording claim 1 in a telecommunications system comprising a radioaccess network, a core network and a mobile equipment wherein thedecisions on whether or not to provide the radio service for theconnection are made in the radio access network and the priority itemsare stored in the radio access network characterized in that the mobileequipment sends the core network entity controlling the bearer a requestto change the value of a priority data item and the core networkrequests the radio access network to change the value of the prioritydata item.
 12. A method according to claim 1, characterized in that atleast a required minimum value for a priority data item is defined andthe bearers having a priority data item value smaller than the requiredminimum priority value are not given resources.
 13. A cellulartelecommunications system, characterized in that for management ofbearers at least two priority data items are arranged to be associatedwith each bearer, the first one of the priority data items having a samevalue for at least two bearers associated under the same clientidentity, decisions whether or not to provide services for a bearer arearranged to be based at least in part on the value of at least one ofsaid at least two priority data items, bearers are organized into setson at least two hierarchical levels and a priority data item is givenfor each set, and all bearers associated with the same client identityhave the same values of a first priority data item of said at least twopriority data items, wherein when considering the denial of servicesbetween first and second bearers, the service is denied for the bearerwith a lower value of the first priority data item, disregarding theirvalues of a second priority data item, unless the bearers have the samevalue for the first priority data item, then the service is denied forthe bearer with a lower value of a second priority data item.
 14. Acellular telecommunications system according to claim 13, characterizedin that at least two sets of decisions on providing service are defined,a first combination of the priority data items is used in a first setand a second combination of the priority data items is used in a secondset.
 15. A radio network controller for a cellular telecommunicationssystem, characterized in that for management of bearers it comprisesmeans for associating at least two priority data items with each bearer,the first one of the priority data items having a same value for atleast two bearers associated under the same client identity, means formaking decisions whether or not to provide services for a bearer isbased at least in part on the value of at least one of said at least twopriority data items; and wherein bearers are organized into sets on atleast two hierarchical levels and a priority data item is given for eachset, and all bearers associated with the same client identity have thesame values of a first priority data item of said at least two prioritydata items; and further wherein when considering the denial of servicesbetween first and second bearers, the service is denied for the bearerwith a lower value of the first priority data item, disregarding theirvalues of a second priority data item, unless the bearers have the samevalue for the first priority data item, then the service is denied forthe bearer with a lower value of a second priority data item.
 16. Aradio network controller according to claim 15, characterized in that itcomprises means for defining at least two sets of decisions on providingservice, means for using a first combination of the priority data itemsin a first set and means for using a second combination of the prioritydata items in a second set.